Capillary column gas chromatography (CC-GC) is an important branch of chemical analysis because of the excellent resolving power and speed of analysis of CC-GC One of the primary characteristics of the columns used in CC-GC is the internal diameter of the column. The use of a relatively small internal diameter column, e.g., 0.1 millimeter, can result in much better resolving power and speed of analysis than the use of a relatively large internal diameter column, e.g., 0.5 millimeter. Nevertheless, the use of relatively large internal diameter columns is increasing because of practical considerations. For example, problems of injection and detection are less complicated with the use of relatively large internal diameter columns. Relatively Large internal diameter columns with thick films are also chosen for applications requiring high capacity or large injections to detect trace components of the sample. However, the high capacity and sensitivity is achieved while compromising speed and separating efficiency, i.e., usually chromatographers must balance or choose between speed of analysis, efficiency and capacity.
It would be desirable to have a column for CC-GC that had the practical advantages of a relatively large internal diameter column and the resolving power, capacity and speed of analysis of the relatively small internal diameter columns.
A multicapillary column for CC-GC comprising thousands of individual columns for capillary preparative chromatography was suggested and then dismissed by Dr. M. J. E. Golay (the inventor of CC-GC) during the opening address at the First International Symposium on Glass Capillary Chromatography in 1975 as reported by Aleksander Janik in the December 1976 issue of Journal of Chromatographic Science on page 589. Golay stated "The second is capillary preparative chromatography. Here, perhaps we make a brief bow to that most theoretical possibility, and go on. Indeed, who would like to manifold a thousand capillaries, all painfully trimmed to the same retention time for a given substance and a given pressure drop, and trust that their properties have been stabilized forever. It is too fantastic."
Despite Golay's negative comments, Janik proceeded to suggest two designs for multicapillary columns. The first was a bundle of wires with the capillary space being between the wires. The second was an assemblage of profiled plates with the capillary space being between the plates.
H. D. Pierce, Jr., et al evaluated the designs of Janik and concluded in an article published in Journal of Chromatographic Science, May 1979, page 297, that the designs of Janik were faulted, e.g., because the capillary spaces were not of circular cross section. Pierce, Jr. et al designed an improved system having seven single glass capillary columns, of about 0.2 millimeter internal diameter each, closely bundled inside a glass tube casing. Pierce, Jr. et al made their multicapillary column by placing seven 1.8 millimeter outside diameter by 1.4 millimeter inside diameter glass tubes inside an 8 millimeter outside diameter by 6 millimeter inside diameter glass tube and then drawing this assembly with a glass tube drawing machine.
Walter Jennings evaluated the design of Pierce, Jr. et al in the book Gas Chromatography with Glass Capillary Columns, Second Edition, 1980, Academic Press, New York, pages 34 and 35, and stated "At our present state of the art, however, it is doubtful whether the phase ratios would be identical in each flow path. This would result in each solute exhibiting a range of partition ratios, resulting in broadened peaks." In the present disclosure a multicapillary column having different phase ratios between at least two of the individual capillaries of the same length, for example, is termed an "unbalanced multicapillary gas chromatography column" and the chromatogram resulting from the use of such an unbalanced column is termed an "unbalanced chromatogram." The above referred to publications are herein fully incorporated by reference.
The state of the art of CC-GC was significantly advanced by the development of fused silica capillary gas chromatography columns in 1979. The fused silica columns are drawn at high temperature, e.g. 2,000.degree. C., using advanced fiber optics technology. The fused silica column is generally also given a polymeric outer coating to increase the break resistance of the column with a polyamide coating being the most popular. The fused silica column is then processed to coat a chromatographically active stationary phase on the inside of the capillary. Fused silica capillary gas chromatography columns are widely available commercially from, for example, J&W Instruments Inc., New Brighton MN.